植物叶片运动的马达器官——叶枕的器官发生分子机制研究

The metabolism, physiology and behavior of plants are orchestrated by diurnal rhythms. The ability to anticipate such circadian rhythms gives plants fitness advantages. The leaves of most species in legume family (Leguminoseae) and wood sorrel family (Oxalidaceae) open during the day and fold at night. Diurnal leaf movement, named nyctinasty, has been of great interest to researchers since Darwin’s time. Nyctinastic leaf movement is generated by the pulvinus, which is a specialized motor organ located at the base of leaf and leaflet. However, the molecular basis of pulvinus organogenesis are largely unknown. In our previous report, petiolule-like pulvinus (plp) mutant lines with defects in leaf movement were characterized in model legume species Medicato truncatula. In this project，the new mutant lines with pulvinus defects were isolated based on the forward and reverse genetics screening. The preliminary data showed that the SCF-MtSAP complex-mediated protein degradation and BR degradation are involved in the pulvinus development. In addition, pulvinus is an abaxialized organ and the establishment of dorso-ventral axis is regulated by two types of transcription factors, respectively. This project is proposed to study the network among these regulators, which will shed the light on the molecular mechanism of pulvinus organogenesis and their biological significance.

植物的代谢，生理和行为受到昼夜节律的精细调控，而植物参与昼夜节律可以使其更好的适应外界环境。豆科和酢浆草科中大部分物种的叶片具有感夜运动的能力，这一现象在达尔文时期就已经被许多科学家所关注。叶片感夜运动是由马达器官——叶枕来控制的，但是叶枕器官发生的分子机制到现在仍然不清楚。我们之前在豆科模式植物蒺藜苜蓿中发现了叶枕发育的关键调控因子PETIOLULE-LIKE PULVINUS (PLP)。在本项目中，我们通过正向和反向遗传学分离了多个新的叶枕发育有缺陷的突变体。初步结果表明，SCF-MtSAP复合体介导的泛素化蛋白质降解过程调控PLP，同时PLP调控油菜素内酯的降解途径来控制叶枕的发育和功能。另外，我们还发现叶枕是一个远轴化的器官，其近轴端和远轴端的极性建立分别受到两类转录因子的调控。本项目拟通过对这些关键因子之间的调控和遗传关系开展研究，阐明叶枕器官发生的分子机制并解析其生物学意义。

我们通过正向遗传学筛选到了mtsap的突变体，发现具有类似plp的叶柄状叶枕的表型。在mtsap突变体的背景下超表达PLP基因，能部分恢复其叶枕表型和叶片运动，说明PLP在遗传学水平上上位于MtSAP，但是MtSAP是如何调控PLP的表达还有待于深入研究。另外我们发现两个极性基因MtAB1和MtAB2也参与调控了叶枕发育，PLP能够在叶枕处激活MtAB1和MtAB2的转录表达，mtab1 mtab2双突变体模拟了plp叶柄状叶枕的表型。进一步的研究发现，PLP与MtAB1和MtAB2存在蛋白互作，协同调控叶枕发育，并且这种互作在豆科植物中是保守的。本研究为解析叶枕的进化机制以及叶片运动的生物学意义奠定基础。